1. Field of the Invention
The present invention relates to a light emitting device including a light source and a wavelength converter in which a semiconductor nanoparticle phosphor is dispersed in a resin formed by polymerization of an ionic liquid including a polymerizable functional group.
The present invention also relates to a wavelength converter in which a semiconductor nanoparticle phosphor is dispersed in a resin formed by polymerization of an ionic liquid including a polymerizable functional group and to a light emitting device including the wavelength converter and a light source.
2. Description of the Related Art
A light emitting device including a semiconductor nanoparticle phosphor has recently been developed as a next-generation light emitting device. By using particles having a nanoparticle size as a phosphor, improvement in light emission efficiency and high color rendering properties as compared with a conventional phosphor are expected. Furthermore, a semiconductor nanoparticle phosphor allows easy control of a fluorescence wavelength, that is, a fluorescence color, based on a change in particle size thereof.
When such a semiconductor nanoparticle phosphor is employed for a wavelength converter of a light emitting device, the semiconductor nanoparticle phosphor should be dispersed in a layer of a solid such as a resin. Unless the semiconductor nanoparticle phosphor dispersed in the resin is protected against external air or moisture, however, efficiency of the semiconductor nanoparticle phosphor will be lowered by influences thereof. Therefore, for example, Japanese Patent Laying-Open No. 2014-169421 discloses a phosphor having a core portion formed of a semiconductor nanoparticle phosphor and a shell portion covering the outside of the core portion and/or filling a gap between the core portions. Japanese Patent Laying-Open No. 2014-169421 uses silica for the shell portion and more preferably uses silica obtained as a result of a condensation reaction of alkoxysilane. With the method described in Japanese Patent Laying-Open No. 2014-169421, however, decreases in efficiency of the semiconductor nanoparticle phosphor have occurred in the step of covering the semiconductor nanoparticle phosphor with silica.
For example, Japanese Patent Laying-Open No. 2014-170938 discloses, as one of light emitting devices including a semiconductor nanoparticle phosphor, a lighting device including a light source, a first phosphor layer disposed on the light source, a quantum layer containing quantum dots (a semiconductor nanoparticle phosphor) disposed on the first phosphor layer, and a second phosphor layer disposed on the quantum layer. According to Japanese Patent Laying-Open No. 2014-170938, with such a lighting device, a desired color and uniformity in output light can be controlled by using the conventional phosphor and quantum dots. According to Japanese Patent Laying-Open No. 2014-170938, the quantum layer can be formed, for example, by applying an uncured base material (a matrix material) such as condensation curable silicone and methyl polymethacrylate with quantum dots (a semiconductor nanoparticle phosphor) being dispersed therein and drying the base material by curing the base material.
When a semiconductor nanoparticle phosphor is employed for a wavelength converter of a light emitting device, the semiconductor nanoparticle phosphor should be dispersed in a layer of a solid such as a resin. In the light emitting device including the semiconductor nanoparticle phosphor, however, for example, when a first phosphor layer is disposed adjacently to the light source and the quantum layer is disposed adjacently to the first phosphor layer as in the example disclosed in Japanese Patent Laying-Open No. 2014-170938, disadvantageously, heat generated from the light source conducts to the wavelength converter including the semiconductor nanoparticle phosphor and thus, the semiconductor nanoparticle phosphor is deteriorated.